1. Field of Invention
This invention relates generally to charging circuits for high voltage batteries, and more particularly to high voltage circuits for a vehicle with an electrified propulsion system.
2. Background Art
Electric and hybrid electric vehicles rely on a rechargeable energy storage system (RESS), such as a high voltage battery or battery pack, to provide power for an electric drive system. While regenerative braking during vehicle operation can re-energize a high voltage (HV) battery to a limited extent, additional battery recharging is also necessary. Accordingly, a typical high voltage battery pack can cooperate with a charger device configured to couple it to a power source such as an electric utility. For example, a charger can plug into an electrical outlet at a residence or charging station to enable battery pack recharging.
A charging process is typically conducted while a vehicle is parked and turned off. In a typical electrical architecture, a RESS can be associated with one or more main contactors for coupling the RESS to the high voltage electrical bus for a vehicle, and one or more charger contactors for coupling the RESS to an electrical charger device. During a typical charging process performed while a vehicle is turned off, the charger contactors are closed while the main contactors are open, allowing energy transfer to the RESS while preventing energy transfer to vehicle systems and devices coupled to the high voltage bus. Similarly, during vehicle operation, the main contactors are closed, coupling the RESS to a high voltage power conversion system and other electrical loads, but the charger contactors are open so that a charger device is not energized during vehicle operation.
A vehicle electrical system can include a DC/DC converter configured to step down the high voltage of the RESS to a lower voltage. It is desirable that the DC/DC converter be configured to provide the stepped down voltage during vehicle operation so that the RESS can energize a low voltage vehicle battery and support various low voltage vehicle devices and accessories. Consequently, a DC/DC converter is often coupled to the high voltage bus on the “vehicle side” of the main contactors so that it is coupled to the RESS when the main contactors are closed for vehicle operation.
However, the charging process itself can require various communications and operations by low voltage devices. In addition, preconditioning operations that require low voltage battery support may be performed during vehicle recharging. For example, a consumer may desire that a vehicle cabin be brought to a desired temperature. Because the main contactors are typically open during the charging process, a DC/DC converter coupled to a high voltage bus on the vehicle side of the main contactors cannot be energized by the RESS during the charging process, and therefore cannot support the low voltage battery and vehicle loads associated with the charging or preconditioning processes. As a result, the low voltage vehicle battery can be drained while supporting the preconditioning process during recharging of the RESS.
A possible solution can include closing the main contactors to energize the high voltage buses that couple the DC/DC converter and other vehicle systems to the RESS. However, this solution would, in addition to coupling the DC/DC converter, couple other systems, such as the propulsion system, vehicle heating and ventilation systems, and other various systems during the charging process. A solution that adds loads that reduce the efficiency of the charging process is generally undesirable. A further solution can include moving the DC/DC converter to the RESS side of the main contactors; however, in this configuration the DC/DC converter would be energized at all times unless additional contactors or protective devices were added. Such a condition is generally undesirable because parasitic loads at the DC/DC converter can drain energy away from the high voltage battery. In addition such a configuration can complicate servicing procedures. Finally, a solution can comprise inclusion of a dedicated DC/DC converter, perhaps integrated with a charger device, configured to operate during a charging process. However, this approach requires duplication of sophisticated circuitry and control, which is redundant and not cost-efficient.